1. Field of the Invention
This invention relates to an improvement in the method of cleaning apparatus used in the processing of semiconductor wafers. More particularly, this invention relates to an improvement in a method used for cleaning semiconductor wafer chemical vapor deposition apparatus.
2. Description of the Related Art
In the deposition of materials on semiconductor wafers by chemical vapor deposition (hereinafter called "CVD deposition") or plasma assisted CVD deposition, coating residues such as, for example, silicon oxide or silicon nitride materials, are deposited on all exposed surfaces in the CVD deposition chamber, as well as the intended deposition on the semiconductor wafer. Such residues, which may accumulate to thicknesses of as much as 0.5 to 10 microns, usually must be removed from the chamber prior to the next deposition.
Conventionally, the CVD chamber is cleaned to remove such residues using a fluorine plasma. While such a cleaning method is effective for removing such undesirable deposition residues, fluorine residues are, in turn, left on the CVD chamber surfaces by such a cleaning step. The presence of such fluorine residues, during a subsequent deposition, may adversely affect the deposited film quality, including poor step coverage, poor reproducibility of runs, and pinholes.
The problem of removing such unwanted fluorine residues has been dealt with in the prior art either by flushing the CVD deposition chamber with an inert gas to eventually remove a sufficient amount of the fluorine residue or by deposition of a thin layer of oxide or nitride over the fluorine residues, e.g., about 500 to 2000 Angstroms of oxide or nitride.
The first such solution to the problem, however, is time consuming, requiring as long as 10 minutes to adequately remove such fluorine residues by inert gas flushing. The second solution to the problem is somewhat self-defeating since the plasma fluorine cleaning step which results in the presence of the fluorine residues is intended to remove such oxide or nitride coatings.
It would, therefore, be desirable to provide an improvement in the method of cleaning CVD deposition apparatus to eliminate or mitigate the deleterious effects of such fluorine residues in the CVD deposition chamber of such apparatus.